recently i discovered doing otc that its possible to buy dirty bitcoins from someone and then when you try to sell it on an exchange the account gets frozen 
does anyone know how to know if a btc is clean this ?
Don't use centralized exchanges and switch to decentralized trading alternatives like Bisq or Robosats, all bitcoins are equal there.does anyone know how to know if a btc is clean this ?
I know there are somn bots and services that can give you some coin rating, but there is no guarantee this would apply to all centralized exchanges, they can freeze your coins and account at any time and for any reason.